Color television picture tube



Nov. 12, 1957 J. c. FRANCKEN COLOR TELEVISION PICTURE TUBE 2 Sheets-Sheet 1 Filed Dec. 10, 1954 llllllll'llll IIII llll'l v INVENTOR JAN CAREL FRANCKEN AG NT 1957 J. c. FRANCKEN COLOR TELEVISION PICTURE TUBE 2 Sheets-Sheet 2 Filed Dec. 10, 1954 INVENTOP JAN CAREL FRANCKEN AGENT 2,813,224 COLOR TELEVISION flCT-URETUBE Jan flarel. Francken, Emmasingel, Ei ifihfl fl lg. Net erlands, assignor, by 'mesne assignmen S,;to,North American .Philips Company, Inc., New York, N- Y., a corporation of- Delaware Application December 10, 1-95,;S'erial N'at4fl45363.

Claims priority, application Netherlands- DecemberlLiQS? This invention relates to devices. for reproducing color :teleyision images and. to a cathode-ray tubefor use in such devices.

vVarious'systems and devices have been proposed for reproducing color television images including semi-electronic, semi-mechanical and fully electronic devices. 'ilfhellatter .usually comprise .a cathode ray tube with a luminescent screen constituted of regularly-arranged discrete surface areas covered with luminescent materials radiating differently-colored light under electron bombardment. A cathode-ray tube used in such systems contains. one or more color-selection electrodes capable of directing the electronbeam to a given surface area radiating the desired color, the color image being built up "by changing the potential applied to said color-selection electrodes. Many different forms of color-selection electrodes. have been proposed. The present invention relates only to devices-in whichcolor-selection is effected meansoftwo grids, hereinafter termed color-selection gridatheactive surfaces of which are constituted only by parallel wires. That is to say, the wires of -each grid extend parallelto each other as well as. parallel to the wires ofthe OthB1 "I lCl. These grids operate in such manner as to produce a focal line on the viewing screen 'whose 'location is determined by the potential of the color selectiongrids. A satisfactory focal line and sufficient intensity of the light radiated by thescreen require a field accelerating the electronsafter passing through the color-selection grids. This field is produced by means of a so-called field electrode which, viewed. from the cathode, is; disposed behind the. color-selection grids. .The fieldelectrode may, for example, consist of a grid,

anelectron-transmitting conductive, e. g. metal, layerpro- 'vided on the screen, conductivematerial mixed with the luminescent material or a self-conductive luminescent material on the: screen. In the last-mentioned three cases, which are. to be preferred overa separate field electrode,

'the latter isconsequently united with the screen to form an assembly. A construction of this type will be described laterby way of example.

As is. customary, to the screen is applied a high D. .6.

potential, usually the highest potentialin the cathode- -ray tube.

In order to obtain a focusing effect between the color-selection grids and the screen, the ratio between the mean or D. C. potential of the colo1 -s ele ction grids and the potential of the screen is required to be 1:4, since under these circumstances the focal point of-the-electron beam just lies on the screen. f luminosity image requires a very high voltage, gene;

able capacitance relative t9. each other, so that the charge 2,813,224 Patented Nov. 12, 1957 through arrangements and equipment producing the colorselection control voltages. The present invention, has as its chief object to. provide a device wherein. low color- -selection voltages are sufficient.

A device in. accordance with the invention for Epicducing color televisionv images Comprises a cathode-"ray tube, and means. for horizontal and vertical scanning of the electron beam, which means; generate a deflection field in the cathode-ray tube. The former comprises. an electron gun, a viewing screen emitting light under electron bombardment, two color-selection grids which are disposed between the screen and the electron gun and having; activesurfaces which consistexclusiyely of parallel wires, and: a field electrode disposed on the sideof the color-selection grids remote from the cathode. The device is further characterized by thefact that the mean or D. C. potential of the color-selection grids does not exceed one-tenth of the potential of-thefield el ctrode. Still further, a fine-meshed grid is provided between the color-selection grids and the field electrode having meshes of a Width at most equal to one-tenth of the spacing between two successive wires of a color-selection grid and a potential at most equal to the mean or D. C. potential of the color-selection grids and not more than 10 volts lower than the lowest potential of a color-selection grid. Finally, a focussing electrode at a potential higher than the mean potential of the color-selection grids and lower than the potential of the field electrode is disposed between the deflection field and the color-selection grids.

The means for lineand image-deflection, i. e., hori zontal and vertical scanning, of the electron beam may, as is known, operate either electroamagnetically or electro-statically. In either case, a deflection field is produced at a patricular area within the cathode-ray tube.

.This deflection field acts upon the electron beam pr-oduced; by the electron gun. In this context, the term electron gun is to be understood to. ma,n. the electrode aggregate producing a concentrated electron beam.

The viewing screen may comprise discrete, evenlydivided surface areas of luminescent materials luminescing in different colors upon excitation by the electron beam. Alternatively, however, the screen may radiate only mono-colored light throughout itssurface and this light may fall on a filtercomprising evenly-arranged discrete surface areas of different spectral transparency or reflection power. In this case, the screen may also be coated with luminescent material or for example, be a so-called incandescent screen; that is to say, a surface heated by the energy resulting from impinging electrons to such a degree as to radiate, light.

Since the color-selection grids conslst exclusively of parallel wires, luminous strips extending parallel to. the direction of the grid wires are produced onthe screen. By applying control voltages to the color-selection grids, the location of these, luminous strips is shifted in a direction at right angles to the direction of the grid wires. Th a iou lum e cen mat al o he sur c are of the filterextend in the vform of strips parallel to the wires of the color-selection grids. i

As h been. stat d ab v the cation o h ino es on he s ree :is det rmined by th P tentials of the color-selection grids, To. this end, suitable control voltages, generally in the-form of stepped waves, are p l ed. t t g ids, Pre b y i pha pp s n. de o ecur a symme ric lefie t Naturally, the geometrical positioning of the two color=selection grids hq mpmtaatfm ob aini g a at sfactory effectas 3 is known, it is most simple to arrange the two grids in one plane so that the wires of one grid alternate with the wires of the other grid. For. the sake of convenience, the invention will be explained, by way of; example, with reference to such a configuration of the color-selection grids, without, however, the invention being'limited thereto.

two different planes. c 7 7 Since, in accordance with the invention, the mean potential of the color-selection grids is not made higher than one-tenth of the potential of the screen, i. e., field electrode, low color-selection voltages will suflice. However, unless special steps are taken, this low potential'will prevent adequate focusing of the electron beam between the color-selection grids and the screen, since in this case the potential ratio between the color-selection grids and the screen is much larger than 1:4. V

In order to re-establish the focusing, a fine-meshed grid might be provided between the color-selection grids and the screen, the grid having a potential substantially corresponding to three times the mean potential of the color-selection grids. If the meshes of this grid are sufliciently small no appreciable concentration occurs thereat. Due to the potential ratio of 3:1, the electron beam is substantially concentrated on the fine-meshed grid, and eventual concentration occurring between the fine-meshed grid and the viewing screen finally results in that focal lines just fall on the screen. However, this 1 method has a serious limitation, because a large'number of secondary electrons is unavoidably dislodged at the color-selection grids and at the fine m eshed grid. All these electrons are accelerated in the direction of the screen Where they give rise to annoying light radiations. Hence, this solution for re-establishing the focusing is objectionable and therefore the invention does not bear relationship thereto.

Another disadvantage accompanyingthe low potential of the color-selection grids is that the electrons have a 'low velocity in a large part of the tube. In order to mitigate this disadvantage, a retarding field is produced between the deflection field and the color-selection grids. Consequently, the electrons retain their high velocity from the deflection field to the retarding field, and, notwithstanding this, they are sufliciently retarded upon reaching the color-selection grids as to readily be controlled by the slight potential variations at said grids. The retarding field may at the same time provide for the focusing by disposing, between the color-selection grids and the screen, a fine-meshed'grid Whose potential is at the most equal to. the mean potential of the oolor-selection grids and is not more than volts lower than the lowest potential of a color-selection grid. In other words, the upper potential limit of this grid is the color-selection grid D. C. potential, and the lower potential limit is 10 volts below the lowest potential attained by a colorselection grid when the color-switching or selecting signals are applied thereto. It is advantageous to make the potential of this fine-meshed grid slightly lower than the potential of the color-selection grids in order to prevent any secondary electrons produced at thecolor-selection grids from reaching the screen.

Extensive investigations have shown that the meshwidth, that is to say, the spacing between the center lines of two adjacent wires of the fine-meshed grid, should at most be equal to one-tenth of the spacing between two successive wires of a color-selection grid Preferably, a normally wound grid is used for the fine-mesh grid,

7 which, consequently, comprises two sets of wires extending in directions at right angles to each other, If desired, it'is suflicient to use wires extending parallelto the wires of the color-selection grids, but since the grid has very fine meshes this'usuallyentails' serious structural difiiculties. Since the fine-meshed; grid unavoidably.

collectselectrons, a grid having a very small shadow ratio is preferably used. -The spacing -between the fine In fact, the two grids may alternatively extendin meshed grid and the nearest color-selection grid, together with the mean potential of the color-selection grids, determines the required strength of the aforesaid retarding field. In the case of a high field strength, the spacing is required to be small but not smaller than is permissible in connection with the capacitance between the fine-meshed grid and the color-selection grids.

- The retarding field between the deflection field and the color-selection grids is produced by an electrode which is disposed between the color-selection grids and the deflection field and has a potential higher than the mean potential of the color-selection grids but lower than the potential'of the field electrode. This electrode, which is termed the focusing electrode, may for example, be a second fine-meshed grid. Alternatively, however, an annular electrode may be used which surrounds a part of the space before the color-selection grids. If desired, these two constructions may be combined.

A further improvement is obtained by dividing the annular focusing electrode into two insulated parts and applying a voltage between these two parts. In this a case, the annular electrode, which is situated at the cathode side, requires a potential exceeding that of the first annular electrode, but at the most equal to the potential of the screen. For the fine-meshed grid, which may be situated at the cathode side of the color-selection grids, it also holds that the width of the meshes should at the most be equal to one-tenth of the spacing between two successive wires of a color-selection grid and that it should have a small shadow ratio. .Naturally, the several electrodes strongly influence the field within the cathode-ray tube in the proximity of the color-selection grids. Several steps may be resorted to inorder to improve the form of said field. This will be explained with reference to the accompanying drawing in which Fig. 1 shows diagrammatically those parts of a device according to the invention for reproducing color images;

Figs. 2 to 7 are detail views of modifications showing different arrangements of the aggregate of color-selection grids, viewing screen, fine-meshed grid and the focusing electrode.

Referring now to Fig. 1, the cathode-ray tube comprises an envelope including a neck 1 and a conical portion 2 secured thereto. The neck 1 contains a beamproducing electron gun 3. Before. entering the conical portion 2, the electron beam is deflected by deflection coil systems 4 and 5 producing a deflection field within the tube. The conical portion 2 of the tube containsa luminescent screen 7 and color-selection grids 8, 9 placed in front thereof and comprising parallel wires extending at right angles to the plane of the drawing. By applying suitable control'voltages to the grids 8 and 9, preferably in phase-opposition as described for example in a copending U. S. application Serial No. 298,942, filed July 15, 1952, the electron beam is directed to a given point of the luminescent screen 7.

The screen 7 is united with the field electrodewhich consists of an electron-transmitting, conductive, for example, metal, layer 6 provided at the cathode side of the screen. The luminescent material, for example, luminescing red, blue and green, extends in the form of strips parallel to the wires of the grids 8 and 9. As is customary in such systems, the said strips alternate in regular succession.

To the viewing screen is applied a high voltage, e. g.

about 15,000 volts, relative to the cathode, the color the space between the deflectionfield and the grids. Disposed behind the colcr s'electio n grids is a fine-meshed select'ion grids and equal to or above apoten-tial 10 volts below the lowest potential of either of said grids. A suitable value'is about 120 volts.

The interacting electrodes '11, 8, 9 and 10 produce such 'a fieldthat each electron beam forms a focal line on the viewing screen-7. As a matter of fact, a retarding lens l-argety responsible for the. focusing is produced between theele'ctrode 11 and the grids '8, 9. Since this 'lensfhas a retarding action, the electrons reach the grids 8, 9 at a low velocity so that they can bereadily controlled-by small voltage variations therein.

Aswill' be appreciated, an annul-arelectrode has shown in Fig. 1 right in front of the .gridsS and 9, particularly ifthey have -largesur'faces, will not yield a uniform field.

Therefore, in one embodiment of the invent-ion as shown .in Fig.2, the annular electrode 11 at the side of the colorselection grids'is closed by means of a fine-meshedgrid 12. In this figure, the remaining electrodes bear the same reference numerals asin Fig. 1. ln order-to reduce the lens effect of the-meshes ofithe grid 12 so as-to avoid any appreciable widening of thefocalrlineon the screen 7, the meshes of .thegrid 12 should at the most have a 'width equal to one-tenth of .the .spacing between two successivewiresof a color-selection grid, the samesas the .grid 10.

'When the electron beam is deflected by the lineand picture-deflection means 4 and 5, the .beam, at the edges of the color-selection grids, is obliquely incident on the planeofthese grids, which results in distortion andblurred edges. In :a device according to the invention, these .errorsare avoided-by .disposing,between-the retarding lens in front of thecoloreselection grids and these grids, a

ring-shapedelectrode whichadjoins theedges of-tb'e surfaces .of the color-selection grids ibllLlS not electrically connected-thereto.

.such that its potential corresponds tothe mean potential of the color-selection grids.

:To this elect-rode,-.a voltage is applied A construction I of this type is shown in-Fig. .3, in which the-electrodes corresponding to those shown in'Figs. l and 2 are provided with the same reference numerals. Aring-shaped electrode 13is 'disposed between the ring-shaped focusing'electrode 11 and the color-selection grids 8, 9, the lens formed be- 'tween-the electrodes land 13 deflecting an obliquely- .incident beam 14ain'suchmanner as to strike the plane of the grids Band-9 substantiallyat rightangles.

A'tfurther improvement upon'the construction shown in Fig. 3 is obtainedby means of the construction depicted inFig. 4Tin which the electrode 11 is covered, on the side remote from the cathode, with a fine-meshed grid corresponding'to the grid 12 in Fig. 2. This construction has -the'advantage over the'construction shownzin Fig. 3 that the lens formed between the electrodes 11 and '13 has 'no parts with negative lens-effect Whereindivergence occurs, contrary tothe 'constru'ctionshown in Fig. 3, because the field has the form shown in broken lines. In the construction shown in Fig. 4, the field is also indicated in broken lines and itisfoundthat by introduction of the grid, only one half of the lens of the construction shown in Fig. 3 remains, and this'half has the desired directional effect on the electron'beam.

Fig. shows another construction in which the electron beam is retarded in twoisteps. lnfront of the electrode 11 is providedan'annular electrode 15 whereof the potential exceeds that of the ring-shaped focusing electrode 11 and at the most corresponds to'the potential of the screen 7, This construction enables greater freedom in choosing the field strength at the cathode side of the colorselection grids. As a matter of f'actythis choice determines the focusing of the electron beam, .the electrode aggregate moreover fulfilling the function ofbendingtthe deflected beam again parallel'to the axis.

The ring-shaped electrode 11 used in the constructions .shown in Figures 1 to '5 may be replaced by a simple, fine-meshed grid disposed in front of the color-selection grids. This construction is shown in Fig. '6. In this case, the fine-meshed grid '1'6'lhas applied to .it a potential exceeding the mean potential of the color-selection grids 8, 9 and lower than, the potential of the screen 7. 'This construction has the advantage that the field strength at the cathode side of the color-selection grids is equal throughout thev grids, which is of importance forsatisfactory focusing throughout the image. In this construction, the electron beam willlbe deflected particularly at the edges of the grid 16 from thecenter of the grid onwards. This is just the reverse of what .is preferably desired, that is to say, the electron beam should reach the color-selection grids at right angles even after deflection. In this case it 'is therefore advantageous to disposea ring-shaped electrode in front of the grid 16, which e'lectrode-isconnected to a point of a source of potential such that its potential is lower thanthat of the grid 16. This construction is shown in Fig. '7 in which corresponding electrodes. are provided with the same reference numerals. A ring-shaped electrode 1 7 having a potential lower than that of they grid 16 is disposed in front of the fine-meshed grid 16 whereof the meshes have a width smaller thanone-tenth of the spacing between two .successive wires. .of a color-selection .grid.

Between the electrode 17 and the wire gauze 16, there isjproduced ajpositive accelerating lens bending the deflected beam parallel tothe axis.

In. order to illustrate a few specific embodiments 'of the'invention, 'theelectrodes of Fig. 1.are spaced as follows fromone another:

Mms. Grid '10'scre'en"6 '8 Grid 10-grids'8 and '9 2 Gridst8.and9electrode11 15 Further, the spacing 'a between the wires of the grid'8 is 1 mm. Thewidth of the meshes of the grid 1-0-is 0.06 mm. The potentials applied to the various electrodes are:

In'the embodiment illustrated in Fig. 6 the values for the'electrodes. 6, 8,9 and '10 are the same as for the corresponding electrodes in the embodiment illustrated in Fig. 1. The width of the meshes of grid .16 is 0.06 mm.,.the distance betweengrid 16 .and the plane of the grids S and 9 is 30 trims. and the potential of grid -16is 5000 volts.

While we have described our invention in connection with specific embodimentsand applications, other modifications-thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. ,A device for reproducing color-television images comprising a cathode-ray tube including an electron gun producing anelectron beam and means producing a deflection' field within the cathode-ray tube for vertically and horizontally deflecting the beam, said tube further including a viewing screen radiating light under electronbombardment, two color-selection grids disposed between the screen and the electron gun and the active surfaces of which consist of parallel wires, and a field electrode disposed on that side 'ofthe color-selection grids remote V ,4. A device as claimed in from the gun; means applying a. given potential to the field electrode; means applying potentials to the colorselection grids at which the mean potential of the colorselection grids does not exceed one-tenth of the potential of the field electrode; said tube also including a fine-mesh grid disposed between the color-selection grids and the field electrode and having meshes of a width equal to at most one-tenth of the spacing between two successive wires of a color-selection grid; means applying to said fine-mesh grid a potential at most equal to the mean potential of the color-selection grids and not more than ten volts below the lowest potential of a colorselection grid; said tube also including afocusing electrode disposed between the deflection field and the colorselection grids; and means applying to said focusing electrode a potential higher than the mean potential of said color-selection grids and lower than the potential of the field electrode.

2. A device as claimed in claim 1 in which the focusing electrode comprises an annular electrode surrounding the space before the color-selection grids.

3. A device as claimed in claim 2 in which a second annular electrode having a potential substantially corresponding to the mean potential of the color-selection grids is disposed between the annular electrode and the color-selection grids.

claim 2 in which, asecond annular electrode having a potential higher than that of the first annular electrode and at the most equal to the potential of the field electrode is disposed between th deflection field and the annular electrode.

5. A device as claimed in claim 1 in which the focusing electrode is a grid the meshes of which have a width at the most equal to one-tenth of the spacing between two successive wires of a color-selection grid.

6. A device for reproducing color-television images comprising a cathode-ray tube including an electron gun producing an electron beam and means producing a deflection field within the cathode-ray tube for deflecting the beam, said tube further including a 'viewing screen radiating lightunder electron-bombardment, two colorselection grids disposed between the screen'and the electron gun and the active surfaces of which consist of parallel wires, and afield electrode disposed on that side of the color-selection grids remote from the gun; means applying a given potential to the field electrode; means applying potentials to the color-selection grids at which the mean potential of the color-selection grids does not exceedone-tenth of the potential of the field electrode;

space before the color-selection gridspmeans applying to said focusing electrode a potential higher than the mean potential of said color-selection grids and lower than the potential of the field electrode; and said tube also including a second fine-mesh grid closing off the end of the annular electrode adjacent the color'selection grids, said second grid having meshes of a width at the most equal to one-tenth of the spacing between two successive 'wires 7 of a color-selection grid.

7. A device for reproducing color=television images comprising a cathode-ray tube including an electron gun producing an electronlbeam and means producing a deflection field within the. cathode-ray tube for deflecting the beam, said tube further including a viewing screen radiating light. under" electron bombardment, two colorselection grids disposed between the-screen and the electron gun and the active surfaces of which consist of .tween the color-selection grids and the field electrode and having meshes of a width equal to at most one-tenth of the spacing between two successive wires of a colorselection grid; means applying to said fine-mesh grid a potential at most equal to the mean potential of the colorselection grids and not more than .ten volts below the lowest potential of a color-selection grid; said tube also including a second fine-mesh grid disposed between the deflection field and the color-selection grids and having meshes of a width equal to at, most one-tenth of the spacing between two successive wires of a color-selec tion grid, and an annular electrode surrounding the space before the second grid; means applying to said second grid a potential higher than the mean potential of said color-selection grids and lower than the potential of the field electrode; and means applying to said annular electrode a potential lower than that applied to said second grid.

8. A device for reproducing color-television images comprising a cathode-ray tube including an electron gun producing an electron beam, a luminescing screen radiating light under electron-bombardment and constituted of a plurality of parallel strips each arranged to produce light in one of a plurality of predetermined colors, and means producing a deflection field Within the cathoderay tube for causing said beam to scan said screen; said tube further including a pair of color-selection grids disposed between the screen and the electron gun and the active surfaces of which comprise parallel wires for causing said beam to selectively impact certain of said strips of said screen, and a field electrode disposed on that's'ide of the color-selection grids remote from the gun; means applying a given potential to the field electrode and means applying potentials to the color-selection grids at which the mean potential of the color-selection grids is less than one-tenth of the potential of the field electrode; and means for retarding said beam and focussing said beam onto said screen including a fine-mesh grid disposed between the color-selection grids and the field electrode and having meshes of a width less than one-tenth of the spacing between two successvie wires of a color-selection V cation of color signals of lowvoltage and power to the color-selection grids is sufficient to produce a satisfactory color image. a

9. A device as set'forth in claim 8, wherein the colorselection grids lie in a common plane and said other electrode is an annular electrode surrounding the space before the color-selection grids.

10. A device as set forth in claim 8, wherein the colorselection grids lie in a common plane and said other electrode is a fine-mesh grid having meshes of a width less than one-tenth of. the spacing between two successive wires of a color-selection grid. 7

References Cited in the file of this patent UNITED STATES PATENTS 2196.127 Kelar Jan. 31, 1950 2,545,123 Tolson Mar. 13, 1951 2,692,532, Lawrence Oct. 26, 1 954 

